In continuous ink jet printing, electrically conductive ink is supplied under pressure to a manifold region that distributes the ink to a plurality of orifices, typically arranged in a linear array(s). The ink discharges from the orifices in filaments which break into droplet streams. Individual droplet streams are selectively charged in the region of the break off from the filaments and charge drops are deflected from their normal trajectories. The deflected drops may be caught and recirculated, and the undeflected drops allowed to proceed to a print medium.
Drops are charged by a charge plate having a plurality of charging electrodes along one edge, and a corresponding plurality of connecting leads along one surface. The edge of the charge plate having the charging electrodes is placed in close proximity to the break off point of the ink jet filaments, and charges applied to the leads to induce charges in the drops as they break off from the filaments. U.S. Pat. No. 4,560,991, issued Dec. 24, 1985, to W. Shutrum, describes one method of fabricating a charge plate. The charge plate taught by Shutrum is fabricated by electro-depositing the charging electrodes and leads on a flat sheet of etchable material, such as copper foil, to form a so-called "coupon." The coupon is bent in a jig at approximately a 90.degree. angle. The leads are then bonded to a charge plate substrate, and the etchable material is removed.
In the prior art, a catcher body was formed by molding, as taught in U.S. Pat. No. 4,857,940 issued Aug. 15, 1989, to Rueping. The top surface of the catcher body was lapped to obtain requisite flatness, and the charge plate was bonded to the catcher body with oven cured epoxy. The area between the bottom of the charging electrodes and the front face of the catcher body was filled with epoxy and a fillet was formed under the charge electrodes using oven cured epoxy. The excess epoxy was then hand crafted under a microscope to remove the excess epoxy. A catcher plate was bonded to the bottom of the catcher body to form a catcher throat.
The tolerances on the charge plate/catcher assembly are critical. In the prior art, assembly steps subjected the part to several steps of heating and curing of epoxy which, due to thermal expansion and contraction of the parts, made the critical dimensions difficult to control. Furthermore, a resistor molded into the catcher body and employed as a heater during operation of the charge plate/catcher assembly to control condensation on the face of the catcher body and the charge electrodes proved difficult to control and produced unstable temperatures in the catcher body capable of distorting the catcher beyond its critical tolerances.
It is seen then that there exists a need for a catcher/charge plate assembly which can be assembled to a very high degree of tolerance.